1. Field of the Invention
The present invention relates to an absorption type heat pump, and more particularly relates to an absorption type heat pump of the GAX (Generator-Absorber Heat Exchanger) cycle in which heat of absorption is used for input heat necessary for regeneration of a strong solution.
2. Related art
The GAX cycle is well known as a technique for enhancing the efficiency of an absorption type refrigerating cycle in which ammonia is used as a cooling medium and water is used as an absorbent. (For example, the technique is disclosed in the documents "A new future for absorption" of ASHRAE JOURNAL November 1986 B. A. Philips).
FIG. 9 shows an example of the GAX cycle of an absorbent liquid shown in the above documents. In the drawing, the process from state F.sub.1 to state C is an absorption process, and the process from state D.sub.1 to state E.sub.1 is a regeneration process.
In the absorption process, water, which is an absorbent, absorbs ammonia vapor, which is a cooling medium, so that a solution in which the cooling medium concentration is high, is provided (condition C). This solution, in which the cooling medium concentration is high, is referred to as a strong solution, hereinafter. Pressure of the strong solution in state C is boosted, and the strong solution is heated when heat is exchanged with the absorption heat generated in the absorption process. In this way, the strong solution is put into a boiling condition and the regeneration process starts (state D.sub.1). In the regeneration process, vapor of the strong solution is boiled and condensed by the heat exchange with absorption heat in the same manner, so that the vapor of the strong solution is put into a state D.sub.2. After that, the strong solution is given heat from the outside of the system by the regeneration heat input device. Therefore, the solution is put into a state E.sub.1 of an ammonia water solution of low concentration and high temperature. This ammonia water solution is referred to as a weak solution.
Since the temperature of this weak solution is high, heat of the weak solution is discharged by the heat exchange so that the discharged heat can be used as a portion of the heat necessary for the regeneration process. While the heat is discharged, the solution is put into an over-cooling condition E.sub.2. Then the pressure is reduced by a pressure reducing valve, so that the solution is put into a state F.sub.1. In this way, the absorption process starts.
The absorption process is defined as a process in which a cooling medium is absorbed by a weak solution of state F.sub.1 so as to generate a strong solution of state C. Absorption heat generated in this absorption process is recovered so as to be used as a portion of heat for regenerating the strong solution generated in the absorption process. Due to the foregoing, the weak solution of state F.sub.l becomes a strong solution of state C, the ammonia concentration of which is increased. Pressure of the strong solution of state C is boosted up again by the solution pump 16, and the above circulation is repeated.
The most important thing to enhance the thermal efficiency in this GAX cycle is to recover absorption heat in the absorption process as much as possible so that the recovered heat can be used for regeneration. In order to attain the above object, it is necessary to provide a wide range of concentration of the solution so as to extend an overlapping portion of the temperature increase in the process of regeneration and the temperature decrease in the process of absorption. In other words, in FIG. 9, it is necessary to extend a temperature difference between states D.sub.1 and F.sub.1, and to reduce a temperature difference between states D.sub.1 and F.sub.2.
State D.sub.1 depends on a temperature of the external cooling fluid for cooling the solution in the absorption process, and state F.sub.1 depends on a limiting line in the ammonia concentration diagram. When the ammonia concentration is 2 to 3% this limiting line is provided That is, a temperature difference between states D.sub.1 and F.sub.1 is approximately determined. Therefore, it is important to reduce the temperature of state F.sub.2. In order to reduce the temperature of state F.sub.2, it is necessary to enhance the performance of the heat exchanger engaging with absorption and regeneration.